July 15, 2009
Dragonflies Top Monarch Butterflies In Longest Migratory Flight
A biologist in the Maldives is claiming that millions of dragonflies fly thousands of miles across the sea from southern India to Africa. If this hypothesis were confirmed, this would be the first known insect migration across open water.
It would also dwarf the notorious Monarch butterfly trip taken annually, as their trip is just half the distance of the dragonflies.Biologist Charles Anderson has written his research over the mass migration in the Journal of Tropical Ecology.
Annually, millions of dragonflies fly to the Maldive Islands, an event that is well known to the locals.
"But no one I have spoken to knew where they came from," wrote Anderson, an independent biologist who works with the Maldivian Marine Research Center.
Their appearance on the island is unusual because the islands that make up the Maldives are quite a distance from southern India, and has practically no surface freshwater, which dragonflies require to complete their lifecycle.
Anderson noticed the dragonflies after his arrival in 1983. He began tracking them every year from 1996 and now collates information gathered by locals in India and on vessels at sea.
After Anderson aligned his data with information from southern India, he developed a progression of dates from north to south, with dragonflies landing first in southern India, moving on to the Maldives, and then on to more southern areas.
The dragonflies first appear in Male in October. Dragonfly numbers are at their highest in November and December, before the insects fly away again.
The dragonflies are obviously flying from India over the open sea to the Maldives, wrote Anderson.
"That by itself is fairly amazing, as it involves a journey of 600 to 800km across the ocean," he says.
How they accomplish this is a mystery, as in October they were flying against the winds. In October, November and December, the Inter-tropical Convergence Zone weather system moves southwards over the Maldives, making their journey easier.
"As there is no freshwater in Maldives for dragonflies, what are they doing here?" asks Anderson. "I have also deduced that they are flying all the way across the western Indian Ocean to East Africa."
Anderson has collected a lot of evidence to support his claim.
Large numbers of dragonflies also began popping up in the northern Seychelles, south of India, in November, and then even further south in December. That matches the movement of the Inter-tropical Convergence Zone system, which blows from India to East Africa.
This suggests that the dragonflies fly with the weather system and monsoon rains to finish a huge migration from India to east and southern Africa, and then back again.
"The species involved breeds in temporary rainwater pools. So it is following the rains, taking sequential advantage of the monsoon rains of India, the short rains of East Africa, the summer rains of southern Africa, the long rains of East Africa, and then back to India for the next monsoon," Anderson said.
"It may seem remarkable that such a massive migration has gone unnoticed until now. But this just illustrates how little we still know about the natural world."
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